1. Field of the Invention
The present invention relates to a visual acuity chart displaying apparatus, and in particular, to a visual acuity chart displaying apparatus which is constructed with a space saving type, using, for example, a concave mirror and a half mirror, and used in a visual performance examination with the state that an eye to be examined is made to view a visual chart image.
2. Description of the Related Art
In the case of a conventional eye examination apparatus constructed with a space saving type using a concave mirror and a half mirror, a manner in which the eye to be examined is made to view a predetermined visual chart image is, for example, as follows.
That is, a visual chart plate in which a large number of visual charts are displayed is disposed on an optical path of a visual chart projecting optical system, and one circular mask plate having a plurality of non-mask portions is disposed rotatably, adjacent to this visual chart plate. Then, by a selection and a combination of a predetermined visual chart of the visual chart plate and a predetermined non-mask portion of the circular mask plate, a visual chart with a predetermined transmission state formed by overlapping the predetermined visual chart with the non-mask portion is to be located on the optical path of the visual chart projecting optical system.
Also, as other example that the eye to be examined is made to view a predetermined visual chart image transmitted by masking, a structure has been known such that two circular mask plates having a plurality of non-mask portions are disposed rotatably in succession, adjacent to the visual chart plate, and then, by a combination of each of the non-mask portions of the two circular mask plates, a visual chart with a predetermined transmission state formed by overlapping the predetermined visual chart with the non-mask portion is to be located on the optical path of the visual chart projecting optical system.
However, in the case of the structure using one circular mask plate in the above conventional eye examination apparatus with a space saving type, since the diameter of the circular mask plate, determined from a relationship between the size of this structure and that of the eye examination apparatus itself is limited in size, the number of non-mask portions to be provided is limited, so that the number of visual chart images with various transmission states to be viewed for the eye to be examined is limited. Thus, there is a problem in that an eye performance examination cannot be performed minutely to be sure. On the contrary, when the number of non-mask portions is increased, since the diameter of the circular mask plate becomes larger, the significance of constructing the eye examination apparatus with a space saving type is reduced.
Also, in this structure, when a visual chart with one transmission state is changed into a visual chart with other transmission state by rotating one circular mask plate, since it is the structure using one circular mask plate, a plural kinds of visual chart images appear to flow with respect to a person to be examined which views a visual chart image as if it flows, so that an uncomfortable feeling is generated in the eye to be examined.
Also, in the case of the structure using merely two circular mask plates, merely a plural kinds of non-mask portions are provided at random in each of two circular mask plates, and a sense performance of a third dimension with respect to the eye to be examined which views a visual chart image with a transmission state is not considered at all. As a result, when two circular mask plates are used, a visual chart with a third dimension, that is, with uncomfortable feeling, is viewed for the eye to be examined. Thus, in this case also, there is a problem in that an eye performance examination cannot be performed minutely to be sure.
The present invention has been made in view of the above problems of the conventional arts, and an object of the present invention is to provide a visual acuity chart displaying apparatus which can be constructed with a space saving type, in which a visual chart image with a predetermined mask state can be viewed smooth and fast without providing the eye to be examined with an uncomfortable feeling, and in which an eye performance examination can be performed minutely to be sure.
According to a first aspect of the present invention, there is provided a visual acuity chart displaying apparatus for displaying various visual charts for a visual performance examination for an eye to be examined, comprising: a visual chart plate in which a plural kinds of visual charts displayed for the eye to be examined are arranged changeably; a first mask plate which is disposed in a front of the visual chart plate with an overlapping state and in which a plurality of non-mask portions for performing each single longitudinal row transmission of the visual charts displayed on the visual chart plate are arranged changeably; and a second mask plate which is disposed in a front of the first mask plate with an overlapping state and in which a plurality of non-mask portions for performing each single transverse column transmission of the visual charts displayed on the visual chart plate are arranged changeably, characterized in that the visual charts with a transmission state can be displayed for the eye to be examined by a combination of a visual chart changing by the visual chart plate and a transmission changing by the first and second mask plates.
According to the first aspect of present invention, since the first mask plate for each single longitudinal row transmission of the visual charts and the second mask plate for each single transverse column transmission are disposed to overlap with each other and then a predetermined transmission is performed outside a predetermined region of the visual charts by a combination of changing in each of the non-mask portions of the first and second mask plates, mask changing with respect to the visual charts can be performed fast and smooth. As a result, the occurrence of the state that the visual chart images viewed by the eye to be examined appear to flow is prevented, and a visual performance examination can be performed without providing the eye to be examined with an uncomfortable feeling.
According to a second aspect of the present invention, there is provided a visual acuity chart displaying apparatus for displaying various visual charts for a visual performance examination, for an eye of a person to be examined, characterized by comprising: a visual chart plate in which a plural kinds of visual charts displayed for the eye to be examined are arranged changeably in a circle; a display optical system for displaying the visual charts of the visual chart plate at a predetermined distance from the eye to be examined; an illumination optical system including a light source for illuminating the visual charts; a mask mechanism including, a first mask plate with a disk shape, which is disposed in a front of the visual chart plate with an overlapping state and in which a plurality of first non-mask portions for performing each single longitudinal row transmission of the visual charts displayed on the visual chart plate are arranged changeably, and a second mask plate with a disk shape, which is disposed in a front of the first mask plate with an overlapping state and in which a plurality of second non-mask portions for performing each single transverse column transmission of the visual charts displayed on the visual chart plate are arranged changeably; indication means for indicating a predetermined transmission state by predetermined visual charts and the plurality of first and second non-mask portions; and a drive system for driving the visual chart plate, the first mask plate and the second mask plate individually to rotate in accordance with indication information by the indication means, so that visual charts with the predetermined transmission state formed by one selected from the group including a transverse direction, a longitudinal direction and a combination of these directions, are displayed outside a predetermined region of the predetermined visual charts.
According to the second aspect of the present invention, when the predetermined transmission state by the predetermined visual charts and the plurality of first and second non-mask portions of the first and second mask plates is indicated by the indication means, the drive system drives the visual chart plate, the first mask plate and the second mask plate individually, so that the visual charts with the predetermined transmission (for example, one character transmission) state formed by one selected from the group including a single transverse column, a single longitudinal row and a combination of these, are located on a visual chart projecting optical system.
Therefore, the predetermined visual chart images with the predetermined transmission state can be displayed for the eye to be examined, the occurrence of the state that visual chart images viewed by the eye to be examined appear to flow Is prevented as in the first aspect of the present invention, and a visual performance examination can be performed without providing the eye to be examined with uncomfortable feeling. Also, since it is constructed by using the first and second mask plates, in comparison with the case where a single mask plate is used, the diameter of each of the mask plates can be made small, and thus a further space saving type can be obtained.